Difference Between Ascent Of Sap And Phloem Translocation
The ascent of sap refers to the upward movement of water and minerals through xylem, driven by transpiration pull and cohesion-tension. In contrast, phloem translocation is the transport of organic nutrients (mainly sugars) from source to sink via the pressure-flow mechanism. Both ensure water and food distribution essential for plant survival.
This Story also Contains
- What is Ascent of Sap?
- Factors Affecting The Ascent Of Sap
- What is Phloem Translocation?
- Factors Affecting Phloem Translocation
- Difference Between Ascent of Sap and Phloem Translocation
- Relationship Between Ascent of Sap and Phloem Translocation
- Ascent of Sap vs Phloem Translocation NEET MCQs (With Answers & Explanations)
- Recommended Video on "Difference Between Ascent of Sap and Phloem Translocation"
What is Ascent of Sap?
The ascent of sap is the upward rush of water and minerals from the root to the leaves through the xylem vital minerals. This is caused by the cohesion tension mechanism.
Mechanism (Cohesion-Tension Theory)
The Cohesion Tension Theory explains the ascent of sap through the xylem. Transpiration creates a negative pressure in the leaf that pulls water upwards. Cohesion and adhesion between water molecules and xylem walls maintain a continuous column. Root pressure provides an additional upward push.
Key Role in Plant Physiology
This ascent of sap is essential in water and mineral supply to the whole plant in conducting major processes like photosynthesis and nutrient uptake that sustain plant health and growth. It also supports turgor and cooling through transpiration.
Factors Affecting The Ascent Of Sap
The ascent of sap is affected by:
Environmental factors
Temperature, humidity and light intensity are important environmental factors that significantly affect the rate of transpiration and hence the ascent of sap.
Higher temperatures and lower humidity increase the rate of transpiration, raising the upward pull of sap.
Plant- Related factors
Other contributing factors include depth of the root, area of leaf and width of xylem.
Plants that have a highly developed root system and big leaf areas are more effective in water uptake and transportation.
What is Phloem Translocation?
Phloem translocation is the transport of organic nutrients, mainly sugars, from the source—mainly leaves—to other parts of the plant through the phloem vessels. The loading and unloading of sugars create pressure differences that result in movement.
Mechanism (Pressure Flow Hypothesis)
The Pressure Flow Theory explains the translocation of sugars through phloem. The pressure gradient exists between the source, where the sugar is loaded into phloem and the sink, where the sugar is removed from the phloem. Translocation involves a combination of active transport and mass flow.
Role In Nutrient Distribution
It makes sure that energy and nutrients are distributed effectively throughout the plant to support the growth, development, repair and storage of reserve nutrients.
Factors Affecting Phloem Translocation
Factors affecting phloem translocation includes:
Physiological factors like temperature affect the rate of metabolic processes that are responsible for translocation.
The pressure gradient formed from the loading and off-loading of the sugars forces the movement of nutrients.
Nutrient flow is further influenced by the concentration gradients from source to sink tissues through the phloem tissue.
Difference Between Ascent of Sap and Phloem Translocation
Aspect | Ascent of Sap | Phloem Translocation |
Definition | The upward movement of water and minerals through xylem. | Bidirectional transport of organic solutes, mainly sucrose, via phloem. |
Purpose | Primarily for water and nutrient transport from roots to leaves. Ensures the distribution of essential minerals and water to support plant functions. | Distribution of nutrients and sugars throughout the plant. Provides energy and building blocks for growth, development, and storage. |
Mechanism | Driven by transpiration pull, cohesion, and root pressure. Water evaporates from leaves, creating a negative pressure that pulls water up through xylem vessels. | Driven by pressure flow and the source-to-sink model. Sugars are actively transported into the phloem, creating a pressure gradient that drives the nutrient flow. |
Structure Involved | Xylem tissues including xylem vessels and tracheids which facilitate water transport. | Phloem tissues including sieve tubes which conduct the flow of nutrients and companion cells support sieve tube function. |
Energy Requirement | It is a passive process, does not require any ATP | It is an active process, requires ATP for sugar loading |
Substances Transported | Water and minerals are transported from roots to leaves. | Sugars, amino acids and hormones are transported from source to sink (can be upward and downward) |
Relationship Between Ascent of Sap and Phloem Translocation
The relationship between ascent of sap and phloem translocation is:
The xylem and phloem work together to maintain homeostasis by ensuring continuous movement of water, minerals and nutrients.
The ascent of sap through xylem carries water from roots to leaves for photosynthesis and transpiration. This upward movement creates the foundation for energy production in plants.
The phloem transport sucrose from leaves to tissues to support growth, repair and energy storages.
The combined activity shows a complete transport network which helps in plant growth and development and homeostasis across all tissues
Ascent of Sap vs Phloem Translocation NEET MCQs (With Answers & Explanations)
The key concepts to be covered under this topic for different exams are:
Mechanism of Ascent of Sap and Phloem Translocation
Ascent of Sap vs Phloem Translocation
Practice Questions for NEET
Q1. Xylem translocates:
Water only
Water and minerals only
Water, mineral salts and some organic nitrogen only
Water, minerals salts and some organic nitrogen and hormones
Correct answer: 4) Water, minerals salts and some organic nitrogen and hormones
Explanation:
The xylem is a type of vascular tissue in plants that transports water, mineral salts, some organic nitrogen compounds, and hormones. It carries water absorbed by the roots to various parts of the plant, along with essential nutrients needed for growth and development. Additionally, certain hormones are also transported through the xylem to regulate physiological processes in the plant. The movement of water occurs primarily through transpiration pull, cohesion-tension, and root pressure. The xylem consists of tracheids, vessels, fibers, and parenchyma, each playing a specific role in conduction and support. The lignified walls of xylem cells provide mechanical strength and prevent collapse under negative pressure. This vascular tissue is crucial for maintaining water balance and structural integrity in plants. Xylem also plays a role in drought resistance by adjusting water transport efficiency.
Hence, the correct answer is option 4) water, minerals, salts, and some organic nitrogen and hormones.
Q2. Why is swelling seen above the ring on the stem whose bark has been removed?
Due to infection
Due to accumulation of water
Due to accumulation of food
All of these
Correct answer: 3) Due to accumulation of food
Explanation:
Ringing Experiment: It was demonstrated by Malpighi with a focus on the phloem and Stephan Hales with a focus on the xylem. A ring of bark was removed from the stem. This removed phloem from the stem and stopped food conduction. However, water conduction continued. Accumulation of the food caused swelling in the cut region. Removal of bark caused a break in the phloem continuum which caused accumulation of food above the ring. This caused swelling.
Hence, the correct answer is option 3) Due to accumulation of food.
Q3. With the girdling experiment, it has been observed that:
Girdling has no immediate effect on transpiration.
Photosynthates accumulate above the girdle.
The bark below the girdle dies.
All of the above
Correct answer: 4) All of the above
Explanation:
Girdling experiment demonstrates the translocation of Photosynthates occurs through phloem. In this experiment, the bark of the tree was removed in a ring around the trunk (called girdling). With this experiment, it has been observed that girdling has no immediate effect on transpiration. However, the transport of Photosynthates in the trunk is blocked at the site where the bark has been removed. Photosynthates accumulate above the girdle. Eventually, the bark below the girdle dies, while the bark above swells and remains healthy.
Hence, the correct answer is option 4) All of the above.
Also Read:
Recommended Video on "Difference Between Ascent of Sap and Phloem Translocation"
Frequently Asked Questions (FAQs)
The process of transport of organic nutrients, mainly sugars, from source to sink—tissues like leaves where they are produced, and various sink tissues like fruits, roots, and growing shoots—is called phloem translocation.
While the rise of sap relies on the mass flow of water driven by transpiration and root pressure in xylem vessels, phloem translocation relies solely on the pressure flow mechanism where differences in pressure between source and sink drive nutrient movement through the sieve tube of phloem
Some of the factors which affect the rise of sap range from
Temperature: A rise in temperature increases the rate of transpiration hence improving the rise of sap.
Humidity: low humidity favours high rates of transpiration hence better flow of water.
Pressure: Pressure developed in the root and that of the atmosphere above affects the water flow in the xylem.
Plant Structure: The anatomy of root structure, leaf surface area and xylem condition affect the effectiveness of the water transport system.
Source-sink model refers to the phloem movement of nutrients. In this model: The source is the part of a plant where the nutrients, chiefly sugars, are manufactured or stored. Example: Leaves Sink: That part of a plant where nutrients are used up or stored. Example: Fruits, roots, growing tissues.
At the source, nutrients are actively loaded into the phloem, creating a high-pressure zone, and this pressure pushes the flow of nutrient-rich phloem sap toward the sink. There, the nutrients either go toward growth or are stored for later use.
Accordingly, xylem and phloem are very vital for plant health since these tissues do some of the critical transportation. Otherwise, it transfers water and nutrients from the roots to other parts of the plants in support of physiological processes like photosynthesis, nutrient uptake, and temperature regulation.
Phloem: This is a tissue transporting the products of photosynthesis away from the leaves, predominantly sugars, to various parts of the plant needing energy, growth, or storage. These combined tissues thus act to fulfil the nutritional requirement of plants, thus helping them in their general growth and survival.
Ascent of sap refers to the stream of water and its dissolved nutrients from the roots upwards to the leaves and the remainder of the plant. It is primarily driven by the process of transpiration through leaves, wherein the process of evaporation generates some form of negative pressure, hence pulling water up through the xylem vessels because of cohesion between the water molecules and the pressure generated by root absorption. This upward move spreads the vital materials to every part of the plant.